Start and post-start corrections in the formation of a fuel-metering signal are known, for example, from U.S. Pat. No. 4,089,317 and are controlled downwardly, that is, the corrections are successively switched off.
The necessity of the start and post-start corrections results from the fuel storage characteristic of the intake manifold. More specifically, injected fuel partially condenses to form a wall film of fuel which adheres to the wall of the intake manifold. Low temperatures and high induction pressures favor the condensation and high temperatures and low intake manifold pressures favor the vaporization of the fuel from the wall film.
The condensation effects a reduction of the fuel quantity inducted into the combustion chamber of the engine. The vaporization increases this quantity. For a cold engine after a start, the influence of the condensation is, as a rule, preponderant which, for example, can be compensated by an increase in the fuel-injection pulsewidth. Basic investigations as to the fuel storage characteristic of wall films are presented, for example, in the article published in SAE Paper 810494.
In addition, a transition compensation UK is used in modern engine controls. This compensation is intended to compensate for the influence of wall film effects on the mixture composition in the combustion chamber during transition between different operating states. Thus, when the throttle flap is opened, an increase of the wall film mass occurs and, when closing the throttle flap, a reduction of the wall film mass occurs.
The fuel metering is correspondingly additionally increased via the injection valves when opening the throttle flap and is greatly reduced when closing the throttle flap in order to compensate for the effect of the fuel flow from the wall film.
This transition compensation is matched to the operationally-warm engine. It has been shown that, in known engine controls, unwanted large incorrect mixture adaptations occur in the time range of the first seconds after a start.
Thus, also significant overenrichment of the air/fuel mixture has been observed under the influence of an increase of the fuel-metering signals as a consequence of the start/post-start corrections under specific conditions.